add encodeData() to SkImageEncoder, and add encoding to SkImage

src/images/SkImageEncoder.cpp

Index: src/images/SkImageEncoder.cpp
diff --git a/src/images/SkImageEncoder.cpp b/src/images/SkImageEncoder.cpp
index 4b52fcdc8c89708852de7da460510aa904ea4455..006a23dff349afc82ba6ac3525104c53b1aa6b10 100644
--- a/src/images/SkImageEncoder.cpp
+++ b/src/images/SkImageEncoder.cpp
@@ -38,3 +38,13 @@ bool SkImageEncoder::EncodeStream(SkWStream* stream, const SkBitmap& bm, Type t,
     SkAutoTDelete<SkImageEncoder> enc(SkImageEncoder::Create(t));
     return enc.get() && enc.get()->encodeStream(stream, bm, quality);
 }
+
+SkData* SkImageEncoder::encodeData(const SkBitmap& bm, int quality) {
+    SkDynamicMemoryWStream stream;
+    quality = SkMin32(100, SkMax32(0, quality));
+    if (this->onEncode(&stream, bm, quality)) {
+        return stream.copyToData();
+    }
+    return NULL;
+}
+